BOOK IX.

384

smelter observe whether the ore is melting too quickly or too slowly, orwhether it is flaming in scattered bits, and not uniting in one mass; in thefirst case the ore is smelting too slowly and not without great expense; inthe second case the metal mixes with the slag which flows out of thefurnace into the forehearth, wherefore there is the expense of melting it again;in the third case, the metal is consumed by the violence of the fire. Each ofthese evils has its remedy ; if the ore melts slowly or does not come together,it is necessary to add some amount of fluxes which melt the ore ; or if theymelt too readily, to decrease the amount.

The second reason is that each time that the furnace is opened with atapping-bar, it flows out into the forehearth, and the smelter is able to testthe alloy of gold and lead or of silver with lead, which is called stannum 16 .When the tap-hole is opened the second or third time, this test shows uswhether the alloy of gold or silver has become richer, or whether the lead istoo debilitated and wanting in strength to absorb any more gold or silver. Ifit has become richer, some portion of lead added to it should renew itsstrength ; if it has not become richer, it is poured out of the forehearth thatit may be replaced witn fresh lead.

The third reason is that if the tap-hole of the furnace is always openwhen the ore and other things are being smelted, the fluxes, which are easilymelted, run out of the furnace before the rich gold and silver ores, for theseare sometimes of a kind that oppose and resist melting by the fire for a longerperiod. It follows in this case, that some part of the ore is either con-sumed or is mixed with the accretions, and as a result little lumps of orenot yet melted are now and then found in the accretions. Therefore whenthese ores are being smelted, the tap-hole of the furnace should be closedfor a time, as it is necessary to heat and mix the ore and the fluxes at thesame time ; since the fluxes fuse more rapidly than the ore, when themolten fluxes are held in the furnace, they thus melt the ore which does notreadily fuse or mix with the lead. The lead absorbs the gold or silver, justas tin or lead when melted in the forehearth absorbs the other unmeltedmetal which has been thrown into it. But if the molten matter is pouredupon that which is not molten, it runs off on all sides and consequently doesnot melt it. It follows from all this that ores rich in gold or silver, when putinto a furnace with its tap-hole always open, cannot for that reason be smeltedso successfully as in one where the tap-hole is closed for a time, so that duringthis time the ore may be melted by the molten fluxes. Afterward, when thetap-hole has been opened, they flow into the forehearth and mix there withthe molten lead. This method of smelting the ores is used by us and by theBohemians.

The three remaining methods of smelting ores are similar to each otherin that the tap-holes of the furnaces always remain open, so that the moltenmetals may continually run out. They differ greatly from each other,

16 Stannum ( Interpretatio ,— werck, modern werk). This term has been rendered through'out as “ silver-lead ” or “ silver-lead alloy.” It was the argentiferous lead suitable for cupel-lation. Agricola, in using it in this sense, was no doubt following his interpretation of its useby Pliny. Further remarks upon this subject will be found in note 33, p. 473.